1. Field of the Invention
This invention relates to an improved process for diazo-type multicolor reproduction. More particularly, the invention relates to a process for diazotype multicolor reproduction using a photosensitive material having a continuous thermoplastic resin pre-coated layer.
2. Description of the Prior Art
It has heretofore been known that when two or more diazonium salts which have different resolving rates and exhibit different hues upon bonding with couplers are used in diazotype reproduction, reproductive copies can be obtained which are colored in two or more hues, depending on the intensity of light on the exposed portions. In such reproductive copies, image colors of the semi-exposed portions are mingled with image colors of non-exposed portions to form a compound color, and the color contrast in the image becomes faded. In such a known reproduction process, it is impossible to reproduce an original having a similar image concentration or light transmission throughout the entire original into different hues.
No diazotype reproduction process has been known by which predetermined portions of an original can be reproduced into hues different from one another regardless of difference or similarity of the light transmission in the original.
In U.S. Pat. No. 3,715,213, a process was suggested for multi-color reproduction, which comprises
A. exposing image-wise a diazotype photosensitive material at actinic light by exposing through an original sheet of an assembly, said assembly consisting of (i) an original sheet having opaque image areas and transparent non-image areas and a layer containing at least one thermovolatile or sublimable azo coupler (a), said layer being on one surface of said original sheet, and coupler (a) being located in only preselected areas which are contiguous with opaque image areas of said original sheet, said preselected areas being present in only a portion of the areas contiguous with said opaque image areas of said original sheet, and (ii) a diazotype photosensitive material having a photosensitive layer containing at least one photosensitive diazonium salt (c), said original sheet (i) being superposed on said diazotype photosensitive material (ii) so that the layer of the azo coupler (a ) comes into face-to-face contact with the photosensitive layer;
B. heating said assembly to thereby heat-transfer said layer of the coupler (a) to the corresponding position on the surface of said photosensitive layer, said steps (A) and (B) being performed simultaneously or in the time sequence of (A) to (B) or (B) to (A); and
C. developing the exposed photosensitive material with an alkali developer in the presence of an azo coupler (b) having a substantially lower rate of coupling with the diazonium salt (c) under the developing conditions than that of the azo coupler (a), to thereby develop said photosensititve material, whereby in the unexposed latent image area of the portion to which the coupler (a) has been heat-transferred, a dye (c)-(a) having a certain hue or color is formed by the selective reaction of the heat-transferred coupler (a) with the diazonium salt (c) and at the same time, in the unexposed latent image areas to which the coupler (a) has not been heat-transferred, a dye (c)-(b) having a different hue or color from said dye (c)-(a) is formed by the reaction of the coupler (b) with the diazonium salt (c), thus producing a multicolored copied image.
Photosensitive materials for diazotype reproduction are usually prepared by coating on a base paper an aqueous solution of a photosensitive diazonium salt optionally containing other additives such as a coupler and a stabilizer. In such copying sheets for diazotype reproduction, the photosensitive composition penetrates into voids of the base paper and even the interior of the base paper is impregnated with the photosensitive composition. Accordingly, a great quantity of the photosensitive composition is required and, moreover, there is a tendency that the contrast in the reproductive copy and the sensitivity of the photosensitive material are lowered.
In order to overcome the above defect, it is common in the art to pre-coat the base paper with an inorganic filler such as silica gel, alumina, titanium oxide and clay, e.g. kaolin, or a combination of such inorganic filler with a high molecule material such as starch, casein, polyvinyl alcohol and polyvinyl acetate emulsion, and to coat a photosensitive composition on the resulting precoat layer. In the art, it is generally known that, in order for the photosensitive composition to be supported on the precoat layer of the base paper, the void-filling precoat layer should be a discontinuous layer of particles. For instance, in Tappi, 48, 55A-59A, Aug. (1965), the following teaching is given:
"The first conception of the precoat principle, i.e., a discontinuous layer of fine particles deposited on the paper surface, is still the basis of the precoating technique" (column 1, page 57A). PA1 A. exposing image-wise to actinic light a diazotype photosensitive material having a photosensitive layer containing at least one photosensitive diazonium salt (c) through an original sheet having opaque image areas and transparent or semi-transparent, non-image areas; and PA1 B. heating a layer containing at least one thermovolatile or sublimable azo coupler (a), which is disposed in face-to-face contact with the photosensitive layer of said photosensitive material, at a preselected area corresponding to an opaque image area of the original sheet desired to be reproduced in a different hue, to thereby heat-transfer said layer of the azo coupler (a) to the corresponding position on the surface of said photosensitive layer; PA1 C. developing the exposed photosensitive material in the presence of an azo coupler (b) having a substantially low rate of coupling with the diazonium salt (c) under the developing condition of that of the azo coupler (a), to thereby develop said photosensitive material, whereby in the unexposed latent image area of the portion to which the coupler (a) has been heat-transferred, a dye (c)-(a) having a certain hue or color is formed by the selective reaction of the heat-transferred coupler (a) with the diazonium salt (c) and at the same time, in the unexposed latent image areas to which the coupler (a) has not been heat-transferred, a dye (c)-(b) having a different hue or color from said dye (c)-(a) is formed by the reaction of the coupler (b) with the diazonium salt (c), thus producing a multi-colored copied image.
Further, in U.S. Pat. No. 3,352,677, there is disclosed a light-sensitive diazotype material for use as diazo intermediate paper, the light-sensitive diazotype material being obtained by impregnating a paper base with a solution of a resin such as polystyrene, polypropylene, etc., in an organic solvent such as toluene, xylene, etc., followed by applying to one surface an aqueous light-sensitive diazotype compound solution.
Moreover, British Pat. No. 1,169,227 discloses a paper sheet having a lacquer coating of a cross-linked hydroxpropyl cellulose ether or a cross-linked hydroxypropyl methyl cellulose ether which can be used as the paper base of a copying sheet. However, by application of the above photosensitive materials having a discontinuous resin pre-coated layer and photosensitive materials disclosed in U.S. Pat. No. 3,352,677 and British Pat. No. 1,169,227 to said multi-color reproduction process, color mixing of the resulting colored image tends to occur (i.e., a turbidly colored image easily forms). In addition, there is the disadvantage of it being difficult to obtain multi-colored copies which may sufficiently satisfy reproduction properties such as concentration, contrast and clearness of the resulting reproductive image.